Method of restoring X-ray film



Patented June 2, 1953 UNITED STATES PATENT OFFICE METHOD OF RESTORIN G X-RAY FILM No Drawing. Application February 23, 1951, Serial No..212,518

4 Claims. 1

This invention relates to a method of restorin X-ray film, particularly age fogged X-ray film.

Manufacturers of X-ray film prescribe the precise storage, handling, and processing conditions for best results with their film. It is understood by users of X-ray film that it must be used within a certain period of time, usually within one year, in order to obtain best results. After that period, and some times during that period, the film becomes age fogged. Age fogged film is film which acquires a deposit of silver grains on the emulsion thereof without any previous exposure to light or radiation. Not all X-ray films age fog with the same rapidity. Usually, slow speed fine grained films age fog more slowly than very fast coarse grained films.

If the film is only mildly age fogged, it is pos sible to retard the fog almost completely without altering the film characteristics appreciably by adding to the developer an anti-fog agent, such as benzotriazole (Kodak Anti-fog No. 1), either alone or in combination with potassium bromide. As the fog density increases, however, this method is no longer effective. Furthermore, this method has disadvantages since different concentrations of the anti-fog agent and potassium bromide are required for different degrees of age fogging. It then becomes impossible to develop age fogged films with fresh films in developing tanks simultaneously. Therefore, it is desirable to have a method of restoring age fogged emulsions prior to exposure thereby eliminating the need fora special developer formulation after exposure.

In the past, when the emulsion was treated before exposure, even mildly treated such as washing in Water followed by drying in a light tight film dryer, there was considerable loss in emulsion speed and contrast.

One of the principal objects of the present invention is to restore age fogged X-ray film prior to exposure so as to restore it substantially to its original characteristics.

Another object of the present invention is to restore age fogged X-ray film prior to exposure so that it may be used in production. This restoring converts metallic silver, which forms on X-ray film during long periods of storage, to photosensitive silver bromide.

Another object of the present invention is to provide a method of reclaiming age fogged. X-ray so that X-ray film may be stored in large quantities for long periods of time without having it become a total loss.

Another object is to restore age fogged X-ray film without extreme losses in emulsion speeds and contrast.

These and other objects and advantages will become apparent hereinafter.

This invention includes treating an age fogged film with a solution containing a mild oxidizing agent. It also comprises the process of restoring age fogged X-ray films which comprises subjecting said films to a mild oxidizing agent, washing, subjecting said film to a clearing bath, Washing, and then drying. The invention further consists in the process hereinafter described and claimed.

This method uses oxidation to restore the fogged silver bromide grains on the emulsion to substah tially the same condition in which they exist in fresh film. While several different oxidizing agents can be used in solutions for this purpose, potassium ferricyanide gives the most satisfactory results. 'Strong oxidizing agents such as potassium permanganate and ammonium persulphate can be used satisfactorily so far as fog removal" is concerned, but these oxidizing agents cause extreme losses in emulsion speeds.

The film to be restored is subjected to a bleaching solution containing potassium ferricyanide for a period of approximately 3 minutes with intermittent agitation by hand. The following bleaching solution has been found to give the desired results: 750 cc. Water, 9 to 11.5 grams potassium ferricyanide, 4.5 to 6 grams potassium bromide, .75 to 1.25 cc. sulphuric acid (concentrated), 15 to 25 cc. wetting agent such as pure di-actyl-sodium-sulfo-succinate' or that sold under the trade-mark Aerosol OT, and sufficient additional water to make 1000 cc.

The following bleaching solution has been found to give the best results:

Water r c c 750 Potassium ferricyanidenl grams 10 Potassium bromide do 5 Sulphuric acid (conc.) cc 1 Wettingagent, such as Aerosol OT (1% solution) cc 2'0 Sufficient additional water to make cc 10'00 Sufficient additional water to ma-l e cc I000 This solution, as well as the bleaching solution,

has good storage properties. The purpose of the clearing bath is to neutralize and quickly remove any excess bleaching solution not removed in the first wash. In both the bleaching solution and clearing bath, the amount of wetting agent may vary with the particular wetting agent used.

After the clearing bath, the film is given a final Wash in rapidly running water for a period of about 5 minutes. The film is then thoroughly dried, without heat, in air. This usually requires about 25 to 40 minutes in still air to prevent streaking and then about 45 minutes in circulating air. If desired, the film can be thoroughly dried in still air, but this takes longer. The film is then ready for use or can be returned to storage.

In this process, all baths and washes should be kept as closely as possible in the temperature range of 65 to 70 F. to prevent excessive swelling of emulsion and to produce restored film of uniform characteristics.

Obviously, the size of the receptacles for the film is a matter of choice depending upon the size and the amount of film to be restored. Pref erably, large tanks are used, although large trays or even large beakers may be satisfactory. Cleanliness is important in all phases of the restoring process.

Experiments show that while there is very little difference between fresh film and age fogged film of the same type restored by this process, the reconditioned film will age fog more quickly than fresh film. Furthermore, for best results, it is recommended that the restored film be developed within 12 hours after exposure, preferably as soon as possible. Care should be taken to keep the total time for the process up to the point of drying from exceeding 12 minutes, since there is considerable loss in emulsion speed after that time.

Obviously, the hereinbefore described process can be used for restoring photographic film as well as X-ray film. It is understood that the ranges in the examples hereinbefore set out for the purpose of illustration would be considerably wider if fog removal alone were desired. However, when restoring the film to its original characteristics, the concentrations of the ingredients of the solutions and periods of time set forth in the examples for subjecting the film to the solutions and washes are highly desirable. The clearing bath and second washing can be omitted if the first washing completely removes the bleaching solution from the film.

This invention is intended to cover all changes and modifications of the example of the invention herein chosen for the purposes of the dis closure, which do not constitute departures from the spirit and scope of the invention.

What we claim is:

1. In a method of restoring an unexposed age fogged emulsion layer comprising substantially completely silver halide to substantially its original condition without substantially affecting the original speed, contrast and latitude, the step which consists in subjecting said emulsion layer to the action of a solution containing a ratio of approximately 750 cc. water, approximately 9 to 11.5 grams of potassium ferricyanide as an oxidizing agent, approximately 4.5 to 6 grams potassium bromide, and sufficient additional water to make 1000 cc. for a period of approximately 3 minutes.

fogged emulsion layer comprising substantially completely silver halide to substantially its original condition without substantially aifecting the original speed, contrast and latitude, the step which consists in subjecting said emulsion layer to the action of a solution containing a ratio of approximately 750 cc. water, approximately 9 to 11.5 grams of potassium ferricyanide as an oxidizing agent, approximately 4.5 to 6 grams potassium bromide, a small but effective amount of a wetting agent such as di-actyl-sodium-sulfosuccinate, and sufficient additional water to make 1000 cc. for a period of approximately 3 minutes.

3. A method of restoring an unexposed age fogged emulsion layer comprising substantially completely silver halide to substantially its original condition without substantially affecting the original speed, contrast and latitude, the step which consists in subjecting said emulsion layer to the action of a solution containing a ratio of approximately 750 cc. water, approximately 9 to 11.5 grams of potassium ferricyanide as an oxidizing agent, approximately 4.5 to 6 grams potassium bromide, and sufiicient additional water to make 1000 cc. for a period of approximately 3 minutes, washing for a period of approximately 2 minutes, subjecting said emulsion layer to a solution containing a ratio of approximately 750 cc. water, approximately 22 to 28 g. sodium bisulfite, and sufficient additional water to make 1000 cc. for a period of approximately 2 minutes, washing said emulsion layer in rapidly running water for a period of approximately 5 minutes, and drying.

4. A method of restoring an unexposed age fogged emulsion layer comprising substantially completely silver halide to substantially its original condition without substantially afi'ecting the original speed, contrast and latitude, the step which consists in subjecting said emulsion layer to the action of a solution containing a ratio of approximately 750 cc. water, approximately 9 to 11.5 grams of potassium ferricyanide as an oxidizing agent, approximately 4.5 to 6 grams potassium bromide, a small but effective amount of a wetting agent such as di-actyl-sodium-sulfosuccinate, and sufficient additional water to make 1000 cc. for a period of approximately 3 minutes,

washing for a period of approximately 2 minutes, subjecting said emulsion layer to a solution containing a ratio of approximately 750 cc. water, approximately 2 2 to 28 g. sodium bisulfite, a wetting agent, and a sufficient additional water to minutes, and drying.

2. In a method of restoring an unexposed age 7 make 1000 cc. for a period of approximately 2 minutes, washing said emulsion layer in rapidly running water for a period of approximately 5 FRANK X. HO-HN. FRANCIS H. HOI-IN.

References Cited in the file of this patent UNITED STATES PATENTS Number Name Date OTHER REFERENCES Ives Dec. 18, 1928 

1. IN A METHOD OF RESTORING AN UNEXPOSED AGE FOGGED EMULSION LAYER COMPRISING SUBSTANTIALLY COMPLETELY SILVER HALIDE TO SUBSTANTIALLY ITS ORIGINAL CONDITION WITHOUT SUBSTANTIALLY AFFECTING THE ORIGINAL SPEED, CONTRAST AND LATITUDE THE STEP WHICH CONSISTS IN SUBJECTING SAID EMULSION LAYER TO THE ACTION OF A SOLUTION CONTAINING A RATIO OF APPROXIMATELY 750 CC. WATER, APPROXIMATELY 9 TO 11.5 GRAMS OF POTASSIUM FERRICYANIDE AS AN OXIDIZING AGENT, APPROXIMATELY 4.5 TO 6 GRAMS POTASSIUM BROMIDE, AND SUFFICIENT ADDITIONAL WATER TO MAKE 1000 CC. FOR A PERIOD OF APPROXIMATELY 3 MINUTES. 